burned!

[orso]

Hi! Took this picture on my ECU board and wonder if its a burned out resistor.

[Dubbie]

Looks like a zener diode.

[Brumby]

My bet also.  Zener diode in MELF package.

IIRC, Dave is a fan of the MELF...

[trys]

Zener next to a wee resistor named Zoe, making fiends with him. They're holding hands.

[helius]

Small glass tubes can be either neons, diodes or capacitors. GDTs (gas discharge tubes, for transient suppression) tend to be quite a bit larger.
Here is a glass cap:

[xavier60]

Hi! Took this picture on my ECU board and wonder if its a burned out resistor.

The part might not be actually bad. It might be running hot normally.

[Brumby]

Small glass tubes can be either neons, diodes or capacitors. GDTs (gas discharge tubes, for transient suppression) tend to be quite a bit larger.

True - but the internal structure plus the markings put the zener clearly at the top of the list.

Hi! Took this picture on my ECU board and wonder if its a burned out resistor.

The part might not be actually bad. It might be running hot normally.

I see some flux residue - but no signs of heat stress.

[viperidae]

Looks like conformal coating, not flux residue.

[mikerj]

Maybe I'm missing something, but why would you think anything is burnt out in the pic you posted?  No obvious signs of heat stress anywhere.

[trys]

I imagine orso saw the black band, and thought it looked like a little burnt out bit.

[orso]

Yes, It looked burned in my eyes, I'm a noob when it comes to components and electronic engineering, but i'm learning (I'm a chemist). Did find some bad soldering on the board that I'm gonna replace. /Thank's for the help.

[trys]

Hey orso, in chemistry, very often if it's black it's burnt.

Trys

[mikerj]

Fair enough, I can see how you could think that if not familiar with that package.  I don't think I've ever seen a burnt-looking glass diode come to think of it.  They usually fail short circuit, though I have seen them light up inside, probably a bond wire glowing

[macboy]

Definitely a normal looking diode in MELF packaging.
I might be wrong, but in my experience usually diodes with a black cathode ring are just silicon diodes. With a blue or other color ring, they are something else like a Zener.  So in this case my bet is not on a Zener as others suggested, just a common diode probably 1N4148 or so.

[KL27x]

^I was curious about this. Maybe they are guessing zener just because of the 2k series resistor. That boosts the odds it's a zener, IMO. (Or maybe just happens to be a reglar diode used to make a reference voltage, lol).

But in MELF, anyhow, all my zeners have a blue band, and the regular signal/rectifiers have a black band. (In the thru hole glass diodes, all mine have come with a black band.)

[Nerull]

There's another thing about zener diodes that can give people a shock - they light up. Not nearly as much as a purpose built LED, but "normal" diodes can give off light too. Zener diodes (or at least some of them) can give off a red color that almost looks like they're burning up.

[floobydust]

MELF's are terrible, they roll off the board during reflow. And they roll off your bench. And they roll on the floor. Crunch.

[Brumby]

But in MELF, anyhow, all my zeners have a blue band...

Hadn't really paid attention to this - but I just checked all my MELF zeners ... and, yes, they have the blue band.

But I have seen MELF zeners online shown with black bands and with yellow bands.  (But that is online)

[KL27x]

MELF's are terrible, they roll off the board during reflow. And they roll off your bench. And they roll on the floor. Crunch.

When I browse the parts on Mouser, some of the manufacturers have a drawing of MELF diodes that are square bodied and round only on the end. But whenever I buy them, they are all the same cylindrical thing. Is this rectangular MELF a real thing, or too good to be true?

I tend to stick with MELF for zeners, anyhow, because it happens to be one of my known commodities. Some SMD diodes I have bought (without looking hard nuff), only to find they have stupid reflow pads that don't wrap around the sides, at all. And many of the ubiquitous SMD black epoxy packages have a stripe that is very hard to see. So for low current diodes, I like MELF for zeners. They are very easy to identify and to solder. The flux keeps them from rolling around, once I place them on the board. Never having to flip them over, this more than negates the rolling, IMO.